1. Technical Field
The present invention relates to a method and an apparatus for referencing or registering a patient or a patient body part in a camera-assisted, medical navigation system.
Surgical operations or radiotherapy are nowadays being performed increasingly with the aid of so-called navigation or tracking systems. In this connection, patient data determined by an imaging technique, for example, by a computer tomography or magnetic nuclear resonance tomography, which is employed to indicate to the treating doctor by means of a display output where his treatment tool is momentarily located. One example application consists, for instance, of displaying the position of the tip of an instrument within a part of the body to be treated in order to be able to precisely operate at the places to be treated.
To enable such a navigation system to function, the momentary location of the patient or the part of the body to be treated needs to be known in situ during treatment. This updated positional data can then be assigned to the data received from the imaging process, for example, the data from a computer tomograph produced some time prior to treatment. After this assignment, the computer-assisted treatment may commence.
2. Description of Related Art
In accordance with the prior art, the aforementioned assignment is achieved with the aid of markers, i.e. with the aid of artificial or natural landmarks on the patient. Thus, German patent No. 196 39 615 proposes sticking artificial markers to the skin of the patient prior to a tomographic scan, use being made of markers which are visible in the tomographic image. After tomography, the patient is brought into the operating room. Upon commencement of treatment, referencing of the patient or his body part occurs in that the markers applied thereto are located by a pointer tool, trackable in the navigation system, in order to make their momentary position known to the computer-assisted system. Once the position of the markers is known, the position of all other points from the tomographic data set can be detected in the updated position of the patient and navigation-assisted treatment can commence.
However, the employment of such externally applied markers to the surface of the skin harbors several disadvantages. For one thing, the skin surface is easily shiftable and such shifts result in inaccuracies during referencing. In particular, when targeting the markers with the pointer tool, the skin may be slightly displaced.
Not too many artificial markers may be employed, however, to compensate such inaccuracies since this delays referencing unnecessarily. Invasive solutions, for example, attaching the markers to the bone substance under the skin, are unpleasant for the patient, while natural landmarks, like for example the root of the nose, often cannot be referenced with good positional accuracy.
Another disadvantage of the above-cited method is especially apparent when the treatment is not performed directly after tomography. Thus, for instance, some of the markers may become detached overnight, which can lead to serious difficulties during referencing. One particularly disadvantageous case materializes when the detached markers are replaced by the patient himself at some other location, which may even result in false treatment.
A further navigation system, based on providing reference markers, is known from U.S. Pat. No. 5,383,454, the system employing actively emitting markers, which are provided separately, and likewise result in the disadvantages as described above.